According to Mormon theology Kolob is the celestial object (Star or Planet is unclear) closest to the sphere of glass or Urim and Thummim on which God dwells. Kolob and God's sphere are both supposed to rotate once in 1000 years so a day with God is as a thousand years with man as the scripture goes. I don't know if these two bodies are supposed to be orbiting around each other or what.

The Earth, by the way, is supposed to be destroyed after the 1000 year reign of Jesus Christ and be converted into a sphere of glass for those who make it to heaven (called "Celestial Glory" in Mormon theology). The rest will have to live somewhere else.